Operation of a blast furnace

ABSTRACT

The use of a lance comprising an inner tube and an outer tube spaced from the inner tube and preferably coaxial therewith, oxygen being passed through the inner tube and hydrocarbon fuel, such as propane, being passed through the gap between the inner tube and the outer tube in the restarting of a blast furnace which has gone cold, the lance being initially present at both the cinder notch and the iron notch of the blast furnace.

. United States Patent 1191 1111 3,819,164 Wells et al. [4 June 25, 1974 [5 OPERATION OF A BLAST FURNACE 2,660,524 11/1953 Abbett et al 75/41 3,199,977 8/l965 Phillips et al. 266/33 R [75] Inventors- 551 5 133 522- f 3,706,549 12/1972 Knuppel et al. 266/35 9 v Scotia, Canada Prima Examiner-Gerald A. Dost 73 A s d s: 10 t ,s d 1 Sslgnee g l gg 32$: [on y ney Attorney, Agent, or Firm-Stevens, Davis, Miller &

Mosher [22] Filed: Oct. 30, 1972 [21] App]. N0.: 301,808

[57] ABSTRACT [30] Foreign Application Priority Data 13 1972 Canada 53869 The use of a lance comprlsmg an lnner tube and an outer tube spaced from the inner tube and preferably coaxial therewith, oxygen being passed through the [52] U.S. Cl 266/29, 266/25, 226666/zl2, inner tube and hydrocarbon fuel, Such as propane, [5]] Int Cl C2") 7/16 being passed through the gap between the inner tube [58] Fieid PP 38 41 and the outer tube in the restarting of a blast furnace 29 b 75/2 6 which has gone cold, the lance being initially present at both the cinder notch and the iron notch of the [56] References Cited blast furnace UNITED STATES PATENTS 5 Claims 1 Drawing Figure 2,468,738 5/l949 Durfee et a1 266/4l OPERATION OF A BLAST FURNACE The present invention relates to the operation of blast furnaces in the production of pig iron and, in particular, the present invention relates to a method of restarting a blast furnace which has gone cold.

Heretofore, when for any number of reasons a blast furnace goes cold during its operation the nonnal method of restoring the furnace to operation is by burning the iron notch and cinder notch of the furnace with an oxygen lance and at the same time putting a small quantity of hot blast through a restricted number of tuyeres in the furnace. This burning is continued until such time as communications are effected firstly between the cinder notch and the tuyeres and subsequently between the iron notch and the tuyeres. This communication allows iron and slag to flow from the furnace and away from the tuyeres while allowing the furnaceto be heated by the injection of hot blast into the furnace coke. This method of restoring the furnace to operation is however, slow and takes many days and sometimes weeks .to restore the furnace to production and is usually accompanied by break outs of iron and slag from the furnace and burning of the tuyeres and coolers in the furnace.

The present invention provides a method of restarting a blast furnace which is rapid desirably taking only a period of hours and in which the tuyeres of the furnace remain substantially undamaged and break outs of iron and slag during startup are minimized.

It has now been found that a blast furnace may be rapidly restarted by injecting a stream of oxygen and hydrocarbon fuel into the cold furnace through both the cinder and iron notches in the furnace such that the fuel stream surrounds the oxygen stream by means of a lance comprising an inner tube and an outer tube surrounding the inner tube which outer tube is preferably heat shielded by a refractory sleeve, the fuel/oxygen ratio in the streams passing through each lance being adjusted so as to initially heat the burden in the furnace and then oxidize it until communication is made be tween the cinder notch and the furnace tuyeres and the iron notch and furnace tuyeres at which point the lances are removed from the furnace and closed and the blast is then restored to the furnace in the normal manner.

According to the present invention therefore, there is provided a method of restarting a blast furnace in the production of pig iron from iron ore which blast furnace has gone cold which comprises inserting in both the iron notch and the cinder notch of the blast furnace a lance comprising an inner tube, and outer tube surrounding said inner tube and providing a space therebetween, sealing said lance in each of said notches to prevent gas escaping therefrom, injecting an oxygen stream into said furnace through said inner tube, injecting a hydrocarbon fuel stream into said furnace through the space between the inner and outer tube such that said hydrocarbon fuel stream surrounds said oxygen stream, varying the fuel oxygen ratio in the stream injected through each notch such that initially the burden in the furnace is heated and then the cold iron in the burden is subsequently subjected to oxidation whereby exothermic chemical reaction occurs to raise the temperature of the iron and slag in the furnace to a point where they are liquefied, removing the lances from the iron and cinder notches of the furnace and restoring the blast to the furnace.

In a particuarly preferred embodiment of the present invention communication between the cinder notch and the tuyeres of the furnace is established first, whence the lance is removed from; the cinder notch and iron and slag is allowed to flow from the furnace through the cinder notch, hot blast is then put into the furnace through said furnace tuyeres and subsequently the lance is removed from the iron notch when communication has been established between the iron notch and the tuyeres of the furnace and thus the iron notch and the cinder notch and the hot blast is fully restored to the furnace.

The lance used in the process of the present invention comprises an inner tube, suitably made of copper and an outer tube, which is preferably coaxial with the inner tube and is suitably made of steel, the outer tube being spaced from the inner tube. A sleeve of high quality refractory material such as high density magnesite is desirably provided around the outer sleeve which protects the tuyere from heat during insertion in the notch. This lance is suitably that described in US. Pat. application Nos 821,802 and 880,892 filed Dec. 12, 1970 by Maxhutte, in which it is used as tuyere to introduce an oxygen stream into a basic open hearth furnace below the surface of the molten metal. It is a critical feature of the present invention that the hydrocarbon fuel, e.g. propane flow through the tuyere at a rate sufficient to provide on dissociation thereof, an entry into the molten metal in the blast furnace sufficient cooling to protect the tuyere and the surrounding refractory lining of the furnace from deterioration. It is generally found that the fuel, e.g. propane should constitute at least 3 percent by volume of the oxygen stream when being used for injection of oxygen into the molten metal for oxidation thereof and preferably should be in the range 3% to 5 percent by volume. However, these ratios are not fixed and are far determined by the size of tuyere for the installation. When the lance is being used initially to melt the iron at the initial starting of the furnace the fuel flow through the lance is increased so as to provide a burning flame, i.e. generate heat for melting the iron. The velocity of the oxygen through the lance should be as high as possible so that the oxidation reaction and the exothermic heat so generated is as far away as possible from the end of the lance and the refractory sleeve.

In the process of the present invention, the lance is inserted at the iron notch and also at the cinder notch and the lances are sealed into the furnace with clay in such a manner that no gases can escape past the lances during operation. An oxygen stream is passed through the inner tube and a fuel, e.g. propane stream passes through the gap between the inner tube and the outer tube. The oxygen and fuel streams are metered to initially supply heat to the furnace burden and then the oxygen fuel ratio is increased to make the injected gas streams oxidize and start a chemical reaction with the cold iron in the furnace which exothermic reaction raises the temperature of the iron and slag in the furnace rapidly to the point where they become liquid. By injecting the fuel and oxygen through both the iron notch and the cinder notch which are both lower than the furnace tuyeres any molten material which is formed does not accumulate around the furnace tuyeres thereby causing damage thereto. Once communications are obtained between the cinder notch and the furnace tuyeres, the lance at the cinder notch is removed and slag and iron is allowed to flow from the furnace through the cinder notch. Hot blast can then be put into the furnace through the furnace tuyeres with the slag and iron being tapped from the cinder notch in the normal manner. During this period the injection of oxygen and fuel is continued through the lance in the iron notch until communications are established between the furnace tuyeres and the iron notch and through the cinder notch and the iron notch at which time the lance is removed from the iron notch with a flow of iron and slag from the furnace. At this stage the cinder and iron notches are closed and hot blast is restored to the furnace in a normal and progressive manner with the furnace coming back into full production. By this method, a blast furnace which has gone cold may be restored to production in a matter of hours with considerable saving in production and cost. The lances of the present invention have the advantage that they do not tend to burn back for the length of time that they are in the cinder and iron notches in the furnace which is a substantial problem with oxygen lances.

The present invention will be further illustrated by way of the following example:

In connection with the accompanying drawing which is a detail side sectional elevation of the hearth of a conventional blast furnace. The conventional blast furnace 1 including a hearth tuyere, an iron notch 3 and a cinder notch 4 extending through the refractory sleeve wall 5. Conventionally the furnace is tapped through the iron notch 3 and excess slag is removed from the furnace through cinder notch 4. The furnace 1 also includes a conventional tuyere through which hot air blast is introduced in that furnace during normal operation.

In accordance with the present invention for restarting such a furnace which has gone cold a lance 6 is inserted both in the cinder notch 4 and the iron notch 3 and is cemented therein. Each lance 6 comprising an inner tube 7 through which a stream of oxygen gas is passed into the hearth two of the furnace through line 7A and an outer tube 8 coaxial with the inner tube 7 providing an annular space 11 through which a stream of propane gas is introduced into the hearth two of the furnace through line 8A. The propane gas stream surrounds the oxygen gas stream on entry into hearth two of the furnace 1 which protects the end of the tuyere and the adjacent refractory wall of the furnace from erosion and disintegration. The outer tube 8 is fitted into a refractory sleeve 9 which serves as a heat shield. The procedure following restarting the furnace l is set forth in the following example:

EXAMPLE A blast furnace of the normal McKee design, having a foot diameter and producing 1,200 tons of molten iron per day at a blast volume of 65,000 S.C.F. of air per minute at a temperature of 1,200 F with a furnace burden for making basic iron consisting of coke, limestone, dolomite, acid pellets and sinter with a coke to burden ratio of 1:25 which had gone cold was restarted over a period of 8 hours by the following procedure:

A lance according to the present invention was inserted both in the cinder notch and iron notch and cemented in place in both notches. Initially, oxygen was introduced into the furnace through each lance at a flow rate of 12,000 cubic feet per hour and at a pressure at the inlet to the lance of lbs. per square inch, and propane was initially introduced at a flow rate of 1,500 cu. ft. per hour the flow rate of the propane being progressively reduced over a period of 4 hours to 500 cu. ft. per hour. At that time, the colour of the furnace as seen through the furnace tuyeres and the build up of slag around the furnace tuyeres indicated that the lance in the cinder notch was having the desired effect and the lance was withdrawn from the cinder notch with a flow of iron and slag from the cinder notch. When the flow of iron and slag stopped the cinder notch was closed and hot blast was introduced into the furnace through the tuyeres in the normal way. The percentage of blast introduced as a percentage of the normal blast was dependent upon the speed with which the furnace began to react, the colour in front of the tuyeres immediately began to improve indicating that combustion of the coke restarted and the blast was increased steadily until the furnace began to move such that iron and slag could be withdrawn from the cinder notch. The cinder notch was then closed with clay and the furnace was periodically opened to allow iron and slag to be withdrawn from the cinder notch and this procedure was continued for a further 4 hours until communication was achieved between the iron notch and the cinder notch whence the iron and slag was capable of flowing from the iron notch which was indicated by the fact that within a given time schedule slag and iron ceased to form around the tuyeres and at the cinder notch.

At this point, with the furnace fully operational, the iron notch lance was removed with both slag and iron flowing from the iron notch. Both the iron notch and cinder notch were then closed and hot air blast introduced through the tuyeres for a period of time whence the iron notch is again opened allowing iron and slag to flow from the furnace. The cinder notch was maintained closed and all the iron and slag was periodically removed from the iron notch. The process was then continued as the temperature of the iron and slag increased and indications of the temperature increase at the opened tuyeres the additional tuyeres were then progressively opened and increasing amounts of hot air blast were introduced until all the tuyeres were opened and the furnace was back to the required temperature and normal operation and normal production was achieved after about one week from restarting.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A method of restarting a blast furnace in the production of pig iron from iron ore which blast furnace has gone cold which comprises inserting in both the iron notch of the blast furnace and the cinder notch of the blast furnace a lance comprising an inner tube and an outer tube surrounding said inner tube and providing a space therebetween, sealing said lance in each of said notches to prevent gas escaping therefrom, injecting an oxygen stream into said furnace through said inner tube, injecting a hydrocarbon fuel stream into said furnace through the space between said inner and outer tube such that said hydrocarbon fuel stream surrounds said oxygen stream, varying the fuel/oxygen ratio injected through the lance in each notch such that initially the burden in the furnace is heated and then the cold iron in the burden is subsequently subjected to oxidation whereby exothermic chemical reactions occur and raise the temperature of theiron and the slag in the furnace to a point where they are liquefied, removing the lances from both the cinder notch and the iron notch when communication has been established between-the notch and the tuyeres and restoring the blast to the furnace.

2. A method of restarting a blast furnace in the production of pig iron from ore which has gone cold which method comprises inserting in both the iron notch of the blast furnace and the cinder notch of the blast furnace a lance comprising an inner tube and an outer tube surrounding the inner tube and providing a space therebetween, sealing said lance in each of said notches to prevent gas escaping therefrom, injecting an oxygen stream into said furnace through said inner tube, injecting a hydrocarbon fuel stream into said furnace through the space between the inner and outer tube such that said hydrocarbon fuel stream surrounds said oxygen stream, varying the fuel/oxygen ratio injected through each notch such that initially the burden in the furnace is heated and then the cold iron in the burden is subsequently subjected to oxidation whereby exothermic chemical reactions occur and raise the temperature of the iron and slag in the furnace to a point where they are liquefied, removing the lance from the cinder notch when communication between the notch and the furnace tuyeres is established, allowing iron and slag to flow from the furnace through said cinder notch, adding hot blast into the furnace, removing the lance from the iron notch when communication has been established between the iron notch and the furnace tuyeres of the furnace, closing the iron notch and restoring the blast to the furnace.

3. A method as claimed in claim 2 in which the fuel is propane.

4. A method as claimed in claim 1 in which the inner and outer tubes of the tuyere are coaxial.

5. A method as claimed in claim. 1 including a refractory sleeve surrounding said outer tube as a heat shield. l 

1. A method of restarting a blast furnace in the production of pig iron from iron ore which blast furnace has gone cold which comprises inserting in both the iron notch of the blast furnace and the cinder notch of the blast furnace a lance comprising an inner tube and an outer tube surrounding said inner tube and providing a space therebetween, sealing said lance in each of said notches to prevent gas escaping therefrom, injecting an oxygen stream into said furnace through said inner tube, injecting a hydrocarbon fuel stream into said furnace through the space between said inner and outer tube such that said hydrocarbon fuel stream surrounds said oxygen stream, varying the fuel/oxygen ratio injected through the lance in each notch such that initially the burden in the furnace is heated and then the cold iron in the burden is subsequently subjected to oxidation whereby exothermic chemical reactions occur and raise the temperature of the iron and the slag in the furnace to a point where they are liquefied, removing the lances from both the cinder notch and the iron notch when communication has been established between the notch and the tuyeres and restoring the blast to the furnace.
 2. A method of restarting a blast furnace in the production of pig iron from ore which has gone cold which method comprises inserting in both the iron notch of the blast furnace and the cinder notch of the blast furnace a lance comprising an inner tube and an outer tube surrounding the inner tube and providing a space therebetween, sealing said lance in each of said notches to prevent gas escaping therefrom, injecting an oxygen stream into said furnace through said inner tube, injecting a hydrocarbon fuel stream into said furnace through the space between the inner and outer tube such that said hydrocarbon fuel stream surrounds said oxygen stream, varying the fuel/Oxygen ratio injected through each notch such that initially the burden in the furnace is heated and then the cold iron in the burden is subsequently subjected to oxidation whereby exothermic chemical reactions occur and raise the temperature of the iron and slag in the furnace to a point where they are liquefied, removing the lance from the cinder notch when communication between the notch and the furnace tuyeres is established, allowing iron and slag to flow from the furnace through said cinder notch, adding hot blast into the furnace, removing the lance from the iron notch when communication has been established between the iron notch and the furnace tuyeres of the furnace, closing the iron notch and restoring the blast to the furnace.
 3. A method as claimed in claim 2 in which the fuel is propane.
 4. A method as claimed in claim 1 in which the inner and outer tubes of the tuyere are coaxial.
 5. A method as claimed in claim 1 including a refractory sleeve surrounding said outer tube as a heat shield. 